Distally extended needles of syringes that have been injected into patients pose risks of injury to medical personnel and of transmitting infectious diseases from accidental needle sticks during handling and disposal of the used syringes. Accidental needle sticks often occur because, for example, the syringe needles are usually relatively small, making them hard to see, and usually very sharp so that slight touches can pierce skin. Contaminated needles can carry blood-borne infectious agents, such as hepatitis B and C, human immunodeficiency virus (HIV), influenza, and tuberculosis, gonorrhea, and syphilis. Infected healthcare workers may transmit infections to patients, coworkers, family members, and others in the community. The Center for Disease Control has issued a recommendation that physicians and nurses avoid recapping used needles.
Various types of safety syringes allowing retraction of the needle from the dangerous extended distal position have been developed over recent years. These safety syringes have a variety of shortcomings including relatively low reliability and relatively high complexity, as well as relatively high manufacturing cost. Even a slight increase in manufacturing cost per syringe can be significant to manufactures and those in a distribution chain dealing with large amounts, perhaps millions, of the syringes per day.
Exemplary safety syringes include those having an internal spring system attached to a barrel of the syringe and to the needle for retracting the needle from its exposed distal position. These spring-loaded syringes are relatively complex and costly.
As another example, a safety syringe exists allowing a user to press a piston of the syringe against a hub connected to the needle and thereby engage the hub so the user can then pull the hub proximally, and thereby pull the needle from the exposed distal position. One problem with a syringe of this type is that it can only be used for a single injection because when the piston reaches a fully injected position, the piston engages the needle hub allowing withdrawal of the needle and the piston together, but disallowing subsequent relative motion between the piston and the needle, which would be required for additional fluid intake/expulsion.